WASHINGTON - The Teamsters Union and other opponents of a Bush administration plan to allow Mexican trucks to roam throughout the United States filed suit in federal court in California this week to stop it from going forward.

The litigation marks the latest effort to block the one-year program, which opponents say would pose a danger to American motorists and a risk to national security.

The lawsuit, filed late Monday in the San Francisco/Oakland division of U.S. District Court, names U.S. Transportation Secretary Mary Peters as a defendant.

In addition to the Teamsters, other plaintiffs include the Sierra Club, Public Citizen, the Owner-Operator Independent Drivers Association and two smaller groups.

The lawsuit charges that the one-year Mexican trucking program, which the administration calls a "demonstration project," is actually a pilot program.

The plaintiffs say the government has failed to comply with the rules for a pilot program - including publishing details of the program in the Federal Register and seeking public comment - and asks the court to prevent the government from going forward until those requirements are met.

Federal officials said last week they plan to certify the first Mexican companies to send trucks into the United States by the end of the month or early May. The administration insists adequate safeguards are in place to protect the public.

Mexican trucks have only been allowed to travel about 25 miles beyond the border since 1982, requiring their cargo to be offloaded into American trucks for further transport.

A provision in the North American Free Trade Agreement was to open the entire United States to Mexican trucks starting in 1995. Access has been delayed over the years by congressional opposition and litigation.

U.S. Transportation Department officials argue the project is not a pilot program and does not have to comply with pilot program rules.

The Federal Motor Carrier Safety Administration responded to the lawsuit in a statement issued Tuesday.

"We have worked extensively with Congress and the Office of the Inspector General to implement this program and its many safety standards and are prepared to defend the program in court," the agency said.

The statement also said the program "will eliminate unnecessary delays clogging commerce at our borders, bring consumers lower prices and give our economy new energy while maintaining the safety of our roads."

Rep. Duncan Hunter, R-Alpine, who has sponsored legislation to block the program, said Tuesday he expected to file a brief in support of the lawsuit.

Hunter "believes the lawsuit has merit, especially when taking into consideration the risks involved in the pilot program," his spokesman Joe Kasper said.

Jonathan Weissglass, an attorney for the plaintiffs, said one reason for believing the project is a pilot program is that Transportation Secretary Peters referred to it that way when she announced it on Feb. 23. Peters also referred to it as a "demonstration program" in the speech.

Similar litigation to block the program was filed in the U.S. Court of Appeals for the 9th Circuit in San Francisco. Weissglass said the lawsuit was filed in both courts because of uncertainty over which court has jurisdiction.

In another development, a provision sponsored by Sen. Dianne Feinstein, D-Calif., which would delay the program, has survived in a House-Senate emergency military spending bill.

That bill is expected to be voted on by Congress this week, but it faces a certain veto from President Bush because it would require U.S. troops to leave Iraq by next year.